In the following, we use \(T\)  to denote a tetrahedron, which is a convex hull of four noncoplanar points in \(\mathbb {R}^3\) . A collection \(\triangle =\lbrace T_1, \ldots , T_N\rbrace \)  of \(N\)  tetrahedra is called a tetrahedral partition of \(\Omega =\cup _{h=1}^N T_{h}\)  provided that any pair of tetrahedra in \(\triangle \)  intersect at most at a common vertex, along a common edge, or along a common triangular face.
In this paper, we restrict our attention to tetrahedralizations of \(\Omega \)  because any polygonal domain of arbitrary shape can be partitioned into finitely many tetrahedra. Without loss of generality, we assume that all the location points \(v_i\) 's are inside tetrahedra of \(\triangle \) , that is, they are not on edges, vertices, or faces of tetrahedra in \(\triangle \) . Otherwise, we can simply count them twice or multiple times if any observation is located on a face, an edge, or at a vertex of \(\triangle \)  [1]}.
